For products all over from industrial apparatuses to home electronics/information terminals, semiconductor devices for electric power are becoming widespread, and with respect to the semiconductor devices for electric power to be installed in the home electronics, they are required to have high productivity and high reliability that allow them to deal with a wide variety of products as well as to be made compact and lightweight. At the same time, they are also required to have a package configuration that is applicable to silicon carbide (SiC) semiconductors which are highly likely to go mainstream in future because of being high in operation temperature and superior in efficiency.
In semiconductor devices for electric power, because they deal with a high voltage and a large current and thus, generate a large amount of heat, there are many cases where a ceramic board that is superior in heat conductivity is used as an insulative board, in order to efficiently release the heat. Further, according to the increase in density of the aforementioned semiconductor element for electric power, a method is becoming put in use in which a copper electrode plate is directly soldered to the main electrode of the semiconductor element for electric power, in order to form a high current-density circuit.
However, a difference in linear expansion coefficient (α) becomes larger according to the combination of an inorganic member such as the ceramic board (α: 6 to 7 ppm/K) and a metal such as the copper electrode plate (α: 16 ppm/K), in comparison with the combination in the case where a conventional resin-based board is instead used. Accordingly, a difference therebetween in expansion/contraction due to temperature change is large, and thus, because of a thermal stress associated with that difference, a crack or like damage is likely to occur, so that there is a risk that the long-term reliability is degraded. For that reason, there has been experimented a method like that in which the periphery of the bonded portion between the copper electrode plate and the semiconductor element is sealed with a soft urethane resin and thereafter the whole is sealed with an epoxy resin, namely, a sealing member is formed in a manner that materials of different physical properties are used differently depending on its regions, to thereby reduce the stress (see, for example, Patent Document 1).